In general, liquid crystal compounds having optical anisotropy (Δ n) and dielectric anisotropy (Δ ∈) are widely used in display devices such as clocks, notebook PCs, mobile phones, televisions and monitors. Such liquid crystal compounds are increasingly in demand. Liquid crystal compounds used in such display devices include a nematic liquid crystal phase, a smectic liquid crystal phase and a cholesteric liquid crystal phase. Among those phases, nematic phases are the most widely used. In practice, various liquid crystal compounds are used in the form of a composition. Liquid crystal compositions should be stable against water, light, heat, air, electric fields or the like, and have to ensure the chemical stability among the compounds forming the composition under the conditions of particular use. In order to use a liquid crystal compound in a display device, the liquid crystal compound should be in harmony of physical properties, including a wide range of liquid crystal phase temperatures, optical anisotropy value (Δ n) and dielectric anisotropy value (Δ ∈), viscosity and conductivity. Properties of a liquid crystal compound required for a display device depend on the specific type of the display device. Therefore, there is an imminent need for a novel liquid crystal device that satisfies the above properties at the same time. Recently, there has been a need for a liquid crystal display device having a fast response time in order to treat a great amount of information promptly.